#include<stdio.h>
int sum(int a,int b)
{
    return (a+b)*(b-a+1)/2;
}
int main()
{
    int a=1;
    int b=100;
    printf("start caculate\n");
    int n=sum(a,b);
    printf("sum=%d\n",n);
    return 0;
}
